A variety of transparent and/or translucent thermoplastic compositions have been developed. Each of those compositions has a particular level of transparency, often characterized in terms of haze, which is expressed as a percentage (%) in accordance with recognized test procedures. However, thermoplastic compositions sometimes exhibit unsatisfactory high haze values (low transparency), poor processability and poor mechanical properties, including undue hardness, low flexibility, etc. For example, previously-proposed thermoplastic elastomer compositions with transparency and flexibility such as compounds based on styrene-ethylene-butadiene-styrene block copolymers, thermoplastic vulcanizate blends (TPV) or thermoplastic olefin (TPO) blends have reached transparency and softness levels that are unsatisfactory in certain applications.
U.S. Pat. No. 6,500,563, for example, discloses blends of two different types of polypropylene, including blends made from a polypropylene having a melting point (Tm) of less than 110° C. and propylene-ethylene copolymer that has isotactically-arranged propylene-derived sequences and Tm less than 105° C.
Three component blends of isotactic polypropylene, impact modifying amounts of an ethylene-propylene-based rubber or low-density ethylene copolymer and a propylene-based elastomer as compatibilizer are described in EP946640, EP964641, EP969043 and EP1098934.
WO04/014988 describes blends of isotactic polypropylene with non-functionalized plasticizers such as poly-alpha-olefins. WO03/040233 also discloses two component blends with the isotactic polypropylene as the predominant, matrix phase and the propylene-based copolymer serving as an impact modifier.
EP1003814 and U.S. Pat. No. 6,642,316 disclose two-component blends of small amounts of isotactic polypropylene and predominant amounts of an ethylene based elastomer. EP0374695 discloses visually homogeneous two component blends however using 40 wt % or less of the propylene-based copolymer. WO 00/69963 describes films made of two-component blends with from 75 to 98 wt % of a propylene ethylene based elastomer having a heat of fusion of less than 25 J/g.
However, such thermoplastic and thermoplastic elastomer compositions are typically prepared with one or more processing aids and/or oils to provide the necessary processability properties for extrusion. Such processing aids and oils over time tend to seep or “bleed out” into the conveyed fluid(s), and contaminate those fluids. As such, tubing used for food contact and medical applications can tolerate very little, if any, bleed. Otherwise, the tubing is not suitable for food contact and medical applications.
There is a need, therefore, for a thermoplastic composition that has a desirable balance of softness, flexibility and strength, and which can be easily processed in a molten state in extrusion or molding without the presence of processing aids and/or oils.